There is a strong requirement, in the field of radio telescope for use in astronomical observation, to use a support mechanism for reflecting mirrors which can achieve and maintain a high mirror surface accuracy.
FIG. 10 is a perspective view showing an example of a conventional reflecting mirror support mechanism. In FIG. 10, reference character 1a designates a plurality of reflecting mirror panels, 2a denotes reflecting mirror support members, and 3a indicates a support base. Each reflecting mirror panel 1a is made and finished so as to have a very high mirror surface accuracy. A plurality of the reflecting mirror panels 1a that are arranged form one reflecting mirror. For example, in a radio telescope for use in astronomical observation a shape of the surface of each reflecting mirror panel 1a is finished so that the main mirror made up of a plurality of the reflecting mirror panels 1a has a desired shape such as a paraboloid of revolution so as to reflect a weak radio efficiently and converg it to the focus of the main mirror.
One reflecting mirror panel 1a is supported by the upper section of each of the three reflecting mirror support members 2a. The lower section of each member 2a is supported by the support base 3a. The support base 3a is made up of a sandwich panel of a CFRP (Carbon-Fiber Reinforced Plastic) with high rigidity, for example.
The conventional support mechanism shown in FIG. 10 uses a well-known three-point support. This mechanism is excellent in structural stability of the reflecting panel 1a. However, because the number of the reflecting mirror support members 2a that support each reflecting mirror panel 1a is small, it is very difficult to perform fine adjustment for the reflecting mirror panels 1a in a desired shape. For example, although the shape of the surface of each reflection mirror panel 1a is made with high accuracy in the field of the radio telescopes for astronomical observation, there happens a necessity to further perform a fine adjustment of the shape of the surface of the reflecting mirror panels 1a, and the fine adjustment is performed in height and support angle of each reflecting mirror support member 2a. However, the actual shape of the surface of each reflecting mirror panel 1a is different from an ideal shape thereof even if the fine adjustment is performed based on the structure where each reflecting mirror panel 1a is supported only by the three supporting points. As a result, there is a possibility that the accuracy of the main mirror as an assembled structure body becomes inferior.
Because the main mirror of a radio telescope for use in astronomical observation has an allowable shape error of not less than several μm, it is necessary to prepare a plurality of small-sized reflecting mirror panels 1a and a plurality of reflecting mirror support members 2a supporting the panels 1a. The panels 1a and the members 2a form the main mirror. In addition to or instead of them, it is further necessary to finish the shape of the surface of each reflecting mirror panel 1a with excellent accuracy. For this reason, the working cost to prepare all the reflecting mirror panels 1a is increased and the work load of the fine adjustment for them is also increased.
FIG. 11 is a perspective view of another example of the conventional reflecting mirror support mechanism. For example, the patent document U.S. Pat. No. 4,750,002 has disclosed such a technique. In FIG. 11, reference character 1b designates reflecting mirror panels, 2b denotes reflecting mirror support members, and 3b indicates a support base. It is so made that each reflecting mirror panel 1b has an excellent mirror surface accuracy. A plurality of the reflecting mirror panels 1b which are arranged form one reflecting mirror.
One reflecting mirror panel 1b is supported by the upper section of each of the reflecting mirror support members 2b of more than three. The support base 3b supports the lower sections of the reflecting mirror support members 2b. The support base 3b is made up of a sandwich panel of a CFRP (Carbon-Fiber Reinforced Plastic) with high rigidity, for example.
In the support mechanism shown in FIG. 11, because each reflecting mirror panel 1b is supported by at least four supporting points, it is possible to easily perform the fine adjustment for the shape of the reflecting mirror panels 1b so that the entire shape of the main mirror becomes an approximately desired shape. However, in a case to use each reflecting mirror panel 1b of a large size it is necessary to greatly increase the number of the supporting points by which each reflecting mirror 1b is supported in order to perform the fine adjustment of the shape of each reflecting mirror panel 1b. This causes several problems to increase the workload for the fine adjustment of the panels 1b and the entire cost of the reflecting mirror because the number of the plural reflecting mirror support members 2a becomes many and the number of the supporting points where the members 2b are mounted on the support base 3b is also increased.
Because the support mechanism shown in FIG. 11 has the structure described above, there is a possibility to happen in each panel 1b a strain caused by a fixture error of each reflecting mirror panel to the support base 3b, a strain caused by a wind load, and a heat strain by a temperature difference between the panels 1b. Further, there is a possibility that those strains cause unexpected deformation between the reflecting mirror panels 1b. 
The present invention has been accomplished in order to solve the aforementioned conventional problems.
An object of the present invention is to provide a reflecting mirror support mechanism capable of supporting the shape of reflecting mirror panels with high structural stability and high accuracy and performing a fine adjustment for the shape of the reflecting mirror panels with high accuracy by low work load. The object of the present invention is also to provide an adjusting method capable of adjusting the reflecting mirror support mechanism efficiently.